A prototype instrument has been constructed and improved which allows the monitoring of blood cultures with an electrical impedance detector. Various problems of unreliability in the impedance detection electronics have plagued this study for a full year. Two of the problems were heat in the 37 degree C incubator affecting components in the circuitry, and an inadequate power supply transformer. The impedance detection apparatus has been moved out of the incubator, and a larger component to supply power has been added.